The use of resonant piezoelectric ceramics to provide linear and rotational motion is well known. The major advantages of such systems is the capability of achieving very fine motion without the use of moving mechanical parts. In general such systems are limited to 1 micrometer of motion accuracy in open loop operation and 50 nanometers in closed loop operation. The velocity is limited to 5 to 10 mm/sec when the weight of a plate to be moved is 0.5 kg. Under these circumstances the force applied to the plate in the direction of motion is limited to about 5N. It would be useful in many situations to achieve better resolution, higher velocities and greater motional drive force for such motors. Improved resolution would be especially useful if the ability to move at relatively high velocities was also preserved.
SU 693493 describes a piezoelectric motor comprising a flat rectangular piezoelectric plate having one electrode covering essentially all of one large face of the plate (the "back" face) and four electrodes each covering a quadrant of the front face. The back electrode is grounded and diagonal electrodes are electrically connected. Two ceramic pads are attached to one of the long edges of the plate and these pads are pressed against the object to be moved by a spring mechanism which presses against the other long edge.
The long and short directions have nearby resonant frequencies (for different mode orders) such that when one pair of connected electrodes is excited with an AC voltage to which the ceramic is responsive, the object moves in one direction, and when the other pair is excited the object moves in the other direction.